A gas turbine installation is a flow machine, essentially comprising a compressor section, a turbine section and a burner section with one or more combustion chambers disposed between the compressor section and the turbine section. During operation of the gas turbine installation ambient air is drawn in by the compressor and compressed to a higher pressure. The compressed air is supplied to the burner section, where it is combusted by means of a burner in a combustion chamber. The combustion waste gas, which is hot and at high pressure due to combustion, is finally supplied to the turbine section as a working medium, where it expands and cools as it works productively, with the energy of the working medium being converted to mechanical work. The energy converted to mechanical work in the turbine section serves on the one hand to drive the compressor and on the other hand to drive a consumer, for example a generator for generating electricity.
In modern gas turbine installations what is known as the premix combustion is generally used. In premix combustion the fuel is first mixed with an oxidation agent, generally air, before the mixture is ignited. During premix combustion a separate mass flow of fuel is also frequently used, being deployed to stabilize the flame and being referred to as the pilot fuel mass flow. The pilot fuel mass flow is fed in by way of a supply system that is separate from the main fuel supply. It serves to protect the flame against instabilities due to the thermo-acoustic response of the combustion process. A premix combustion, in which a pilot gas flow is used, is also referred to as piloted premix combustion. In piloted premix combustion the NOx emission of the combustion system is generally a function of the quantity of the pilot fuel mass flow supplied. The smaller the pilot fuel mass flow, the smaller too the NOx emission.
A combustion chamber with a burner configured for piloted premix combustion is described for example in US 2005/0016178 A1. The burner is surrounded by a burner insert, with an annular gap that opens toward the combustion chamber interior being present between the burner insert and the burner. The annular gap is sealed off from the combustion chamber exterior. The combustion chamber insert comprises a carrier and a burner insert wall located in front of the carrier toward the combustion chamber interior and at the same time forming the combustion chamber wall in the area of the burner. In order to be able to cool the burner insert wall, a cooling air duct is formed between the burner insert wall and the carrier, being supplied with cooling air from the combustion chamber exterior. This cooling air duct is sealed off from the annular gap between the burner insert and the burner. At the end of the burner insert away from the burner there is also an aperture to the combustion chamber interior, by way of which the cooling air flowing through the cooling air duct is discharged into the combustion chamber interior.